Misfiring on over-run

[Blurredman]

Hi guys,

It's been a while since I've posted here, but in honesty, i've only just come accross issues with my MZ for over a year. Mind you, it has mostly been in the garage not doing alot but going out once in a blue moon


Anyway, a problem has arisen lately whereby on the over-run, the bike misfires. It doesn't totally die however.

Other than that, the bike seems to pull fine, no misfires pulling away, nor at a cruising pace. The issue only occurs when de-accelerating. In that time, I notice it is pulsing a considerable amount more than it used to.

I wanted to ask the views on others before I tackle the problem. I was going to have a look at the points last night, but lack of space in the garage in the cold meant I couldn't be bothered (and the bike was working enough until today, or the weekend at least so I didn't want to mess with it while it is my commuter machine for now; dropped the Honda CX500 at the petrol station breaking the front brake lever-woops). I did however take the opportunity to (not just lubricate the chain, but..) clean any liquid around the points area, give them a brief sanding in situe and lubricate the felt on the cam not that that would make any difference.

I've checked for air leaks in the manifold and carburettor but no issues there it seems.

The spark plug is a nice tan/brown colour. (Ever since going iridium i've never needed to touch the spark plug for fouling- , but that's beside the point)


Thanks !

Blurredman

[DAVID THOMPSON]

2 stroke or 4 stroke some of the 660 motor are bad about that on deceleration
dave

[Blurredman]

'87 ETZ 250. I must put it in my sig



Tonight I set up the points as appropriate to what the book says, and my current arrangement with the cylinder head being 1mm further than 3mm due to the clearances required by the unofficial 300cc kit I have installed.

12thou opening at the points. Kicked back powerfully initially, a bit more tinkering with advance/retarding and it starts first kick for the most part now. I did have to turn the idle down, it was running at 3k rpm.. So the timing (or point gap) must have been quite a bit off if i've got it set up correctly now.


I hope to go out on it tomorrow and see how it performs.

[DAVID THOMPSON]

not had very many 2 smokers but found them a bit fussy on the timing an plugs...

and a stock pipe usually plays better than most aftermarket junk these days.
dave

these bikes are good daily drivers and hot rodding them is a disservice to there usefulness
if the main ride is down for service

[Blurredman]

I use stock pipe, have been for the last two years Dave.

I've obviously timed the bike incorrectly because although it runs, it was a little flat in places, I compensated by adding more fuel, but eventually the bike doesn't idle. And while in the process of dying the engine seems to run backwards. There is also spats of oil dribbling from the oil filler cap The spark plug is also dry and a light black with no sign of the nice brown.

How on earth do you set these things? Haynes is absolutely useless (as we all know) and the official MZ handbook is a little vague as to what constitutes the advance/retard. I've not messed with the timing before on this bike. The car I own is simple to set with a timing lamp.


This is annoying. However not necessaryily immediate, today the arrival of my replacement brake levers came for the CX500, so i've got my main ride all set again




**EDIT**



Quick update, after removing the plate that covers the front sprocket and where the points are. I collected all my tools and found a quiet length of road not too far from me where there are no neighbours to annoy..

Eventually, after a couple of tests, stops, re-timing I found the setting that gives the least flat spots on the rev range and it is apparent that the adjustment plate is pretty much fully forwards, and it is actually more or less exactly what the plate's position was before I messed with it. The difference now I seem to remember is that the points actuate a larger gap, and in my opinion (but i've yet to prove) It may have been the lack of gap in the appropriate degree the points that could have been causing misfire.


I will hopefully don my motorcycle clothes and go on a run with it today, if not tomorrow and conclude my results.

[DAVID THOMPSON]

feed that cx500 lots of fresh clean oil and filters

the ones we had here in the states would loose the crank if you neglected the oil and filters

a small change in gap can make several degrees in the timing

dave

[Blurredman]

Right, after FINALLY realising my timing still wasn't right, I tried it again from the start. And did some proper reading this time to brush up on how to do it properly.

3 steps are all that is required, and it goes like this:

1) Find the point at which the points gap is it's largest, unfortunately the mark on the cam lobe no longer existed, but I got it. Once you've found it, set the points gap to 0.3mm.

2) Find 3mm before top dead centre. I use a lolly pop with marks on it indicating top, then reverse the engine to the higher mark on the stick indicating 3mm before TDC.

3) Set ignition timing. Do this with a spare bulb and battery and some wires. I used one of my spare 6v battery and 3w bulbs. Make a curcuit with the bulb and battery with the points in the middle. Find the point on the ignition plate that hovers the bulb in an off/on state. And tignten it all up.

Done.

I got this so wrong when I tried to set it up the other month. I was setting the points gap at the same time as the engine was at 3mm < TDC and got it all arse-backwards.

It now runs beautifully, never so well before in my ownership. Pulls very well. Not least because it has an iridium spark plug, 1 tooth lower front sprocket and a 300 barrel and piston means it can roll on the throttle (on flat ground) in fourth from 2.5k very nicely, quite a bit of torque to play with! Very pleased now!



Don't worry about the CX, as much as it looks like an oily, dirty piece of poop it is very mechanically sound with just shy now of 69k miles. I put new oil and do filter every 5k miles at intervals of 55/60/65/70k so that I remember easily. It does need a new air filter now though, and when it gets to 70k it will get new plugs too! It also needs new tyres, front still has a little left with 14.5k on it. Rear needs changing now with 10k. Good machine, done 10k on it this year.